[clang][Interp] Remove faulty assertion

The assertion doesn't work if there are multiple declarations for
a variable involved.

Author: tbaederr

clang/lib/AST/Interp/Program.cpp

@@ -169,7 +169,6 @@ std::optional<unsigned> Program::getOrCreateDummy(const ValueDecl *VD) {
 
 std::optional<unsigned> Program::createGlobal(const ValueDecl *VD,
                                               const Expr *Init) {
-  assert(!getGlobal(VD));
   bool IsStatic, IsExtern;
   if (const auto *Var = dyn_cast<VarDecl>(VD)) {
     IsStatic = Context::shouldBeGloballyIndexed(VD);

clang/test/AST/Interp/literals.cpp

@@ -1209,4 +1209,16 @@ constexpr int externvar1() { // both-error {{never produces a constant expressio
 namespace Extern {
   constexpr extern char Oops = 1;
   static_assert(Oops == 1, "");
+
+#if __cplusplus >= 201402L
+  struct NonLiteral {
+    NonLiteral() {}
+  };
+  NonLiteral nl;
+  constexpr NonLiteral &ExternNonLiteralVarDecl() {
+    extern NonLiteral nl;
+    return nl;
+  }
+  static_assert(&ExternNonLiteralVarDecl() == &nl, "");
+#endif
 }